1. Technical Field of the Invention
The present invention relates to a pump capable of performing an ideal air removal action in pressure zones from atomospheric pressure zones to high vacuum zones, and in particular relates to a multiple-type pump that possesses the function of a turbo-molecular pump which transfers air in high vacuum zones in a highly efficient manner, and the function of a screw type pump which compresses air and transfers it in atmospheric pressure zone.
Uses for this multiple-type pump invention include the emptying of the vacuum chamber of CVD equipment used in the manufacture of semiconductors. Further, the multiple-type pump, according to this invention, is used for compressing air in the atmosphere and transferring the compressed air to an air intake system of an engine or a fuel cell.
2. Background Art
(The Screw Type Pump)
The screw type vacuum pump is one which is well-known among the conventional vacuum pumps. For example, a known one, described in the Japanese Laid-open Publication No. Sho 60-216089, is a kind of screw type pump used from low vacuum zones, known as sliding flow zones, to high vacuum zones, known as free molecule zones, and has superior air evacuation capabilities in low vacuum zones.
In other words, screw type pumps are highly efficient in the evacuation of air in low vacuum zones and are capable of high-speed air evacuation, but experience a decrease in air intake volume and a lowered air evacuation efficiency in high vacuum zones. However, in the vacuum pumps used as air evacuation units in the CVD equipment used in the manufacture of semiconductors, they are required to possess superior air evacuation characteristics not only in low vacuum zones, but also in high vacuum zones.
(The Technology of (J01) Described in Japanese Examined Patent Publication No. Hei-6-92799)
The following is a known prior art (J01) that is described in Japanese Examined Patent Publication No. Hei-6-92799 which aims to fulfill the above-mentioned requirement. Described in this publication is a screw type vacuum pump whose air intake volume in high vacuum zones was increased for the purpose of improving its air evacuation efficiency in high vacuum zones.
The screw type vacuum pump mentioned in this publication has a groove width correlation {groove width/(thread width+groove width)} of 0.8-0.95 in its upstream edge portion in the direction of the air conveyance, and attempts to increase the air intake volume at its upstream edge by increasing the groove depth as it goes toward the upstream edge.
(Problems Relating to the Above-mentioned Prior Art (J01))
The air evacuation efficiency of the above-mentioned prior art did not actually increase in the high vacuum zones to the degree anticipated. The reasons for this are not clear, but probable causes such as the following can be assumed:
(1) When speaking of a screw type pump which has inferior air evacuation capacity in high vacuum zones, a reason for which its air intake volume in high vacuum zones does not increase can be explained by the design for vacuum pumps which originally came from screw type pump theories relating to direction of air transfer, from the upstream edge to the downstream edge. In other words, in turbo-molecular pumps, which have a high air transfer capacity in high vacuum zones, vanes are used for air transfer that, if strong, the thinner they are, the more volume of air they can take in, and the greater the air evacuation capacity. In screw type pump theory, however, no matter how the screw grooves and screw threads of the upstream edge portion were to be designed, the air intake capacity in high vacuum zones would not increase.
(The Turbo-Molecular Pump)
In contrast to the above-mentioned screw type pumps, turbo-molecular pumps, like those disclosed in patent publications and the like, such as in Japanese Examined Patent Publication No. Sho 50-27204, have superior air transfer characteristics in high vacuum zones.
That is, turbo-molecular pumps have a casing with a cylindrical inner surface, wherein lies a rotor which rotates around the rotary shaft of the shaft of the above-mentioned casing. On the inner surface of the above-mentioned casing, multiple fixed vanes (static vanes), arranged along the circumference, are arranged in a multi-level fashion at prescribed intervals in the direction of the shaft. On the outer surface of the above-mentioned rotor, multiple dynamic vanes, arranged along the circumference, are arranged in a multi-level fashion in the direction of the shaft. The above-mentioned static vanes and dynamic vanes are slanted in relation to the above-mentioned rotary shaft, and the tilt angle (vane angle) decreases from the upstream side to the downstream side.
Each level of each of the static vanes and dynamic vanes, which are placed in multi-level fashion at intervals in the direction of the above-mentioned shaft, is placed alternately in the direction of the shaft and organized in such a way as to take the air brought from the upstream edge going in the direction of air transfer and transfer it to the downstream side by virtue of the rotation of the above-mentioned dynamic vanes.
The air evacuation efficiency of a turbo-molecular pump such as this is high in high vacuum zones, but the problem with it is that its air evacuation efficiency in low vacuum zones is low.
Another problem is the use of large numbers of static vanes and dynamic vanes, which means a large number of parts, and a construction that is complex and costly. Still another problem is the ease with which the above-mentioned static vanes and dynamic vanes become dirty.
(The Multiple-Type Vacuum Pump)
Conventionally, multiple-type vacuum pumps that are a combination of the screw type pump and the turbo-molecular pump have been known, and it was hoped that a vacuum pump would be created capable of achieving a highly efficient air evacuation rate in low to high vacuum zones by bringing together the advantages of the above-mentioned screw type and turbo-molecular pumps. The technology for such multiple-type vacuum pumps, as in the following (J02), for example, are well known in the art.
(J02) is xe2x80x9cAn Easy to Understand Vacuum Technology (Compiled and written by the Japan Vacuum Association, Kansai Branch; Published by the Japan Vacuum Association, Kansai Branch, pg. 91xcx9c99, published Jun. 23, 1995)
This (J02) prior art relates to a multiple-type vacuum pump that combines a screw type pump with a turbo-molecular pump, by placing the turbo-molecular pump on the upstream side of the screw type pump. The air taken in by the turbo-molecular pump on the upstream side is compressed and transferred to the screw type pump on the downstream side. For this reason, the screw type pump, which performs air evacuation with low efficiency in high vacuum zones, is able to take the air which has been compressed by the turbo-molecular pump on the upstream side and transfer it to the downstream side with great efficiency.
(Problems Associated with the Aforementioned Prior Art (J02))
The foregoing prior art (J02) requires that numerous static vanes and dynamic vanes be manufactured and placed at many levels in the direction of the shaft of the turbo-molecular pump and installed at prescribed locations. This results in high manufacturing costs.
Moreover, the structure of the turbo-molecular pump portion is complex, so that when it is used in CVD equipment as an air evacuation device, or when it expels a large quantity of reactive air which has not reacted with anything, it provides many places where side reaction product can easily stick and build up. Side reaction product sticks and builds up easily on the static vanes of turbo-molecular pumps, for example. The result is a multiple-type vacuum pump whose durability may be greatly deteriorated.
The applicants of the present invention learned from the problems associated with the above-mentioned conventional multiple-type vacuum pump, and have developed the following technology (J03) which has already been on the market for some time.
((J03) Multiple-type Vacuum Pump shown in FIG. 16 and FIG. 17)
FIG. 16 is a drawing showing the side view of the rotor of the multiple-type vacuum pump which the applicants of this invention have developed and have had on the market for some time. FIG. 17 is a cross-sectional view taken along the line XVIIxe2x80x94XVII of FIG. 16 above.
The multiple-type vacuum pump 01 in FIG. 16 and FIG. 17 has a casing with a cylindrical inner surface 02a and a rotor 03 which rotates around a rotary shaft of the shaft of the above-mentioned cylindrical inner surface. On the outer surface of the rotor 03 is formed an air transfer portion 04 which transfers air in the direction of the shaft at the time of rotation. In the above-mentioned air transfer portion 04, a screw type pump air transfer portion 05 is provided in a downstream portion in the direction of air transfer and a turbo-molecular type pump air transfer portion 06 of the upstream portion. Between the above-mentioned screw type pump air transfer portion 05 and the turbo-molecular type air transfer portion 06, there is provided a ring connector 07 formed as ring-shaped concave grooves.
The above-mentioned screw type pump air transfer portion 05 includes multiple screw threads 05a which are formed as a spiral and at circumferentially prescribed intervals in the above-mentioned downstream portion of the outer surface of the above-mentioned rotor 03, and screw grooves 05b formed in between each of the aforementioned multiple screw threads 05a. The above-mentioned turbo-molecular type pump air transfer portion 06 includes multiple vanes 06a formed at a slant in relation to the direction of the rotary shaft and at circumferentially prescribed intervals, and air transfer grooves 06b formed between each of the above-mentioned multiple vanes 06a. 
In the (J03) multiple vacuum pump 01, constructed as described above, air which has been taken in from the upstream edge at the time of rotation is compressed by the turbo-molecular air transfer portion 06 and transferred to the upstream edge of the above-mentioned screw type pump air transfer portion 05. Different from the ordinary turbo-molecular pump, which has static vanes to and dynamic vanes arranged in a multi-level fashion and placed alternately in the direction of the shaft, the turbo-molecular type pump air transfer portion 06 has only vanes that correspond to the first-stage dynamic vanes of the upstream edges of the ordinary turbo-molecular. pump. For this reason, the turbo-molecular type air transfer portion 06 has a simple construction and is easy to manufacture.
(Problems to be Solved)
The multiple vacuum pump 01 of the prior art (J03) with its capacity as such has been sold on the market for nearly thirty years. The reason why the above-mentioned (J03) multiple vacuum pump has sold for over such a long period of time is because, over a period of many years, there has been no multiple vacuum pump with a capacity of epoch-making proportions, although various efforts have been made, in the vacuum pump industry to develop a new multiple vacuum pump.
In the multiple vacuum pump 01 which uses the foregoing prior art (J03), the inventors of the present invention were interested in knowing what the air flow conditions, at the ring connector 07 part formed by the aforementioned ring-type concave groove, would be like if the turbo-molecular pump air transfer portion 06 on the upstream side were connected to the screw type air flow transfer portion 05, and conducted a simulation using a supercomputer in order to find out. The results of the simulation showed a smoother air flow and improved air transfer efficiency.
Based on the results of the simulation, a multiple-type vacuum pump was made such that the downstream edges of the vanes 06a and the air transfer grooves 06b of the turbo-molecular type pump air transfer portion 06 on the upstream side were connected to the upstream edges of the screw threads 05a and the screw grooves 05b of the screw type pump air transfer portion 05 on the downstream side. When this simulation was done, it was possible to achieve, in a verifiable manner, nearly double the capacity as compared to the above-mentioned conventional multiple-type vacuum pump (J03), (i.e., the capacity to discharge air in xc2xd the time of the conventional multiple-type vacuum pump).
Further, the foregoing multiple-type vacuum pump made by the applicant of this invention, when used in the atmosphere, can compress and transfer air to an air intake system of an engine or a fuel cell, since it has a compression function.
In view of the foregoing problems and the test results of the experimental products, the following (O01) relates to the technical object of the present invention.
(O01) To provide a multiple-type pump that not only achieves a very fast air exhaust speed in the atmospheric pressure to high vacuum zone range, but also has a simple construction and superior durability.
Described below is the present invention and how it solves the above-mentioned problems. However, in order to make it easier to correlate the constituents of the application examples below with the constituents of this invention, there is appended a list of numerical and other symbols in brackets that correspond to the constituents of the application examples. Meanwhile, correlating the symbols of the application examples that follow to the present invention was done in order to facilitate understanding of the invention, and not to limit the scope of the present invention to the embodiments set forth in the specification.
In order to resolve the above-mentioned problems, the present multiple-type pump invention was equipped with the following constructional requirements (A01)-(A04) which represent its distinct features.
(A01) A rotor (H), which rotates around rotary shaft (J) that is concentric with a casing (6) within the casing (6) that has a cylindrical inner surface and whose air transfer portion (S), which transfers air in the direction of the shaft at the time of rotation, is formed on the outer surface;
(A02) The air transfer portion (S), having a turbo-molecular type pump air transfer portion (S2) of the upstream portion in the direction of ;air transfer, and a screw type pump air transfer portion (S1);
(A03) The screw type pump air transfer portion (S1), which transfers, to the upstream side, air that has flowed into the upstream edge at the time of rotation, and which includes multiple screw threads (36), formed as a spiral and with a width of more than 5 mm and placed at prescribed intervals circumferentially in the downstream portion of the outer surface of the rotor (H), and screw grooves (37) formed between each of the multiple screw threads (36);
(A04) turbo-molecular type pump air transfer portion (S2), comprising multiple vanes (41) having fixed vane angles (xcex8) formed at prescribed intervals circumferentially in the upstream portion of the outer surface of the rotor (H) and air transfer grooves (42) formed in between each of the multiple vanes (41), where upstream edge vane widths (W1) of the vanes (41) are each formed to be 3mm or less, while downstream edges of the vanes (41) are formed so as to be continuous with the upstream edge of the screw threads (36), a downstream edge at the base of the air transfer portion (42) formed so as to be continuous with the upstream edge of the base of the screw grooves (37), and takes air that has been brought down from the upstream edge at the time of rotation, compresses it and then transfers it to the upstream edge of the screw type pump air transfer portion (S1).
(Description of the Constructional Requirements of the Invention)
In the present invention described above, the above-mentioned xe2x80x9cturbo-molecular type pump air transfer portion (S2)xe2x80x9d refers to the member equipped with the following constructional requirements (A04):
(A04) xe2x80x9cTurbo-molecular type pump air transfer portion (S2)xe2x80x9d, comprises air transfer grooves (42) formed between multiple vanes (41) having fixed vane angles (xcex8) formed at prescribed intervals circumferentially in the upstream portion of the outer surface of the rotor (H) and each of the multiple vanes (41), the vanes (41) whose upstream edge vane widths (W1) are each formed to be 3 mm or less and whose downstream edge is formed so as to be continuous with the upstream edge of the screw threads (36), where a downstream edge at the base of the air transfer portion (42) is formed so as to be continuous with the upstream edge of the base of the screw grooves (37), and takes air that has been brought down from the upstream edge at the time of rotation, compresses it and then transfers it to the upstream edge of the screw type pump air transfer portion (S1).
The constructional requirements (A04) of the above-mentioned turbo-molecular type pump air transfer portion (S2) differ from the constructional requirements of ordinary turbo-molecular pumps. One of the differences, for example, is that while the thickness of the dynamic vanes in the upstream edge portion in ordinary turbo-molecular pumps is uniform at both the upstream and downstream edges, the vanes (41) of the turbo-molecular type pump air transfer portion (S2), according to the present invention, are of varied thicknesses at the upstream and downstream edges.
In the detailed description of this case, the term turbo-molecular type pump air transfer portion (S2) is used relating to the above-mentioned constructional requirements (A04) which differ from the constructional requirements of the above-mentioned turbo-molecular pump. This is because, one can use turbo-molecular design theory, as described below, to make a broad range of designs.
Notwithstanding, it is not necessary to use turbo-molecular pump design theory when designing the above-mentioned turbo-molecular type pump air transfer portion (S2). For instance, as disclosed in the screw type pump of Japanese Examined Patent Publication No. Hei-6-92799, it would also be possible to design a turbo-molecular type air transfer portion (S2) equipped with the above-mentioned constructional requirements (A04) by making the screw threads of the upstream portion narrower as they go to the upstream side.
The detailed description in the present application uses the term xe2x80x9cturbo-molecular type pump air transfer portion (S2)xe2x80x9d in reference to the member that has the constructional requirements (A04), and therein explains the design methods following turbo-molecular pump design theory, but this is in no way meant to place limitations on the construction of the conventional turbo-molecular pumps.
The vanes (41) of the turbo-molecular type pump air transfer portion (S2) are members comprised of the dynamic vanes of the upstream edge portion of ordinary turbo-molecular pumps (e.g. first- or second-stage dynamic vanes), and have the same function as these dynamic vanes (the function whereby air is taken, compressed and transferred downwardly). Additionally, the vanes (41) of the turbo-molecular type pump air transfer portion (S2) are similar in form to the dynamic vanes of the upstream edge portion of ordinary turbo-molecular pumps. Furthermore, with regard to the approximate values of air evacuation volume, air compression ratio, etc., in the turbo-molecular pump type air transfer portion (S2) of the present invention, it is possible to calculate approximate values from the contour parameters of the turbo-molecular pump air transfer portion (S2) by using ordinary turbo-molecular pump design theory.
The vanes (41) of the turbo-molecular type pump air transfer portion (S2) correspond to the dynamic vanes of the upstream edge portion in ordinary turbo-molecular pumps (e.g. the first- and second-stage dynamic vanes), and the same function is demanded of them as those of the foregoing dynamic vanes of the upstream edge portion. In other words, the spacing chord ratio (So/b), determined by the spacing So and length b between each of the multiple vanes (41), is set within the range of 0.8 less than (So/b) less than 1.2, the same as for the dynamic vanes (e.g. the first- and second-stage dynamic vanes) of the upstream edge portion of the turbo-molecular pump. Furthermore, the thinner the vanes (41) of the turbo-molecular type pump air transfer portion (S2) are, the larger the square measure of the opening is, so it is desirable to make them thinner, in the same fashion as in the dynamic vanes of the upstream edge portion of the foregoing ordinary turbo-molecular pump, so long as the strength can be maintained. Further, the vanes (41) have an overall plate shape, but it is possible to add somewhat of a twist to the vanes (41), or to provide them with a little curved or bent portion in the upstream or downstream edge portions. Particularly in the case where the vane angle (xcex8) of the vanes (41) and the tilt angle of the screw xcex11 of the upstream edge of the screw type pump air transfer portion (S1) are xcex8 greater than xcex11, it is desirable to provide a little curved portion in the downstream edge portion of vanes (41) for the purpose of making smooth the connection between the downstream edge of the vanes (41) and the upstream edge of screw threads (36).
In addition, it is possible to provide the turbo-molecular type pump air transfer portion (S2) with additional vanes (43, 44) other than each of the multiple vanes (41) formed so as to connect the downstream edge with the upstream edge of the screw threads (36). The additional vanes (43, 44) can be disposed between each of the adjacent vanes (41) spaced from each other circumferentially, or disposed at the upstream side of each of the vanes (41).
During the normal rotation of the multiple-type pump (P), according to the present invention, it is desirable to design such that the air transfer volume (cubical flow volume, air evacuation volume) at the downstream edge of the turbo-molecular type pump air transfer portion (S2) be equal to the air transfer volume (cubical flow volume, air intake flow volume) of the upstream edge of the screw type pump air transfer portion (S1) of its downstream side. In that case, it is possible to calculate the air evacuation volume of the turbo-molecular type pump air transfer portion (S2) of the present multiple-type pump invention (P) using the same calculation methods used to determine the air transfer volume of the dynamic vanes in the upstream edge portion in ordinary turbo-molecular pumps.
It is, therefore, possible to design the turbo-molecular type pump air transfer portion (S2) whose air transfer volume (cubical flow volume and air evacuation volume) in its downstream edge is equal to the air transfer volume of the upstream edge of the screw pump type air transfer portion (S1).
Moreover, at the time of design development, it is possible to, for example, design the vanes (41), if it has a little curved portion at its upstream or downstream edge portions, to be a flat plate without regard to the curved portion. And if unsuccessful in achieving a trial product with the capacity anticipated, it would be possible to modify the design according to the results of computer simulation, testing, and experimentation, and the like, to develop a high capacity product.
In high vacuum zones, known as molecular flow zones, the occurrence of air molecules colliding into one another is infrequent. Rather, it is the frequency of collision of the air molecules against the walls surrounding them that governs the movement of the air molecules. For this reason, in order to improve a pump""s air evacuation capacity, within the range of a pressure zone (a high vacuum. zone), the important factor is what degree of efficiency the air molecules fed into the pump""s air intake opening can be transferred out to the air outlet. Since the volume of in-coming air molecules is proportionate to the square area of the air intake opening, enlarging the square area of the air intake opening is a useful means for increasing air evacuation velocity. Nevertheless, enlarging, without care, the square area of the opening increases in-coming air molecules, which, in turn, increase the return of air molecules, with the result that the air evacuation velocity cannot be increased, thereby degrading compression capacity. For this reason, to achieve the targeted air evacuation speed, it is advantageous to utilize the above-mentioned theoretically established turbo-molecular pump design methods in regard to air evacuation efficiency and compression capacity, in order to establish the appropriate square area of the opening while maintaining a steady level of air evacuation efficiency and compression capacity. It is advisable that the surface of the connector portion of the downstream edge of the turbo-molecular type pump air transfer portion (S2), and the upstream edge of the screw type pump air transfer portion (S1) be joined together in a smooth manner.
When, for example, a base diameter, a diameter of a circle that includes a circumference of the base (the connector portion where vane (41) joins the air transfer grooves(42)) of the vanes (41) that lie in a cross-sectional plane perpendicular to the rotary shaft (J), and to the base of the screw threads (36) (the connector portion where screw thread (36) joins the screw grooves (37)) is small at the upstream edge and large at the downstream edge of air transfer portion (S), it is favorable that the base diameter be changed, along the axial direction, in a smooth manner. By doing this, the radiuses from the center of the rotary shaft (J) are the same, allowing for a smooth connection between the base of the downstream edge of air transfer grooves (42) of the turbo-molecular type pump air transfer portion (S2), and the base of the upstream edge of screw grooves (37) of the screw type pump air transfer portion (S1).
In addition, since the vanes (41), having a thickness of 3 mm or less at the upstream edge of the turbo-molecular type pump air transfer portion (S2), need to be made the same thickness, at the downstream edge, as the width of the screw threads (36), the thickness of the vanes (41) is increased as they progress toward the downstream side. Thus, a smooth connection can be created between the downstream edge of the vanes (41) and the upstream edge of the screw threads (36), which is favorable. In this case, the thickness of the downstream edge of the vanes (41) is equal to the width of the upstream edge of the screw threads (36), and the width of the downstream edge of the air transfer grooves (42) is equal to the upstream edge of the screw grooves (37).
In doing this, it is possible to avert the harmful effects on a lowering of air evacuation efficiency arising from a disturbance in the flow of air due to abrupt changes in the shape between the turbo-molecular type pump air transfer portion (S2) and the screw type pump air transfer portion (S1).
Further, in the present invention, it is also possible to dispose a turbo-molecular pump (50) having multiple dynamic vanes (51a, 52a) and static vanes (53a, 54a), located at the further upstream side of the upstream edge of the turbo-molecular type pump air transfer portion (S2) and arranged in an alternate fashion in the direction of air transfer. In that case, it is possible to improve the air evacuation capacity in an ultra-high vacuum zone of the multiple-type pump (P).
(Operation of the Invention)
The rotor (H) of a multiple-type pump, equipped with the above-mentioned construction, according to this invention, rotates within the casing (6) having a cylindrical inner surface, and around the rotary shaft (J) coaxial with the casing (6). The air transfer portion (S) formed on the outer surface of the rotary (J), has the turbo-molecular type pump air transfer portion (S2) of the upstream portion of the air transfer direction, and the screw type pump air transfer portion (S1) of the downstream portion.
The turbo-molecular type pump air transfer portion (S2) has multiple vanes (41), which are arranged circumferentially at prescribed intervals in the upstream portion of the rotor (H) and have prescribed vane angles (xcex8), and air transfer grooves (42), which are formed between each of the multiple vanes (41). Since each of the vanes (41) are made with a vane thickness (W1) of 3 mm or less in the upstream edge, the square area of the upstream edge opening becomes large, thereby taking in a larger air volume. The turbo-molecular type pump air transfer portion (S2) takes air that has been drawn in from the upstream edge at the time of rotation, compresses it and transfers it to the upstream edge of the screw type pump air transfer portion (S1).
Thus, the turbo-molecular type pump air transfer portion (S2), like ordinary turbo-molecular pumps, can transfer air in high vacuum zones in a very efficient manner.
The downstream edge of the vanes (41) of the turbo-molecular type pump air transfer portion (S2) is connected to the upstream edge of the screw threads (36). In addition, the downstream edge of the base of the air transfer groove (42) is connected to the upstream edge of the base of the screw grooves (37). With this structure, the air being transferred to the downstream side, through the air transfer grooves (42) of the turbo-molecular type pump air transfer portion (S2), can pass through the connector portion of the downstream edge of the air transfer grooves (42) and the upstream edge of the screw grooves (37) without any significant disturbances.
Therefore, the air that has been transferred from the turbo-molecular type pump air transfer portion (S2) is able to flow into the screw type pump air transfer portion (S1) in a compressed state and without being accompanied by a significant reduction in speed or rise of pressure at the upstream edge of the screw type pump air transfer portion (S1).
The screw type pump air transfer portion (S1) has multiple screw threads (36), spiral in shape, and formed circumferentially at prescribed intervals at the downstream portion of the outer surface of the rotor (H), and screw grooves (37) formed between each of the multiple screw threads (36), and transfers the drawn-in air to the downstream side at the time of rotation. Since the screw threads (36) have a width of 5 mm or more, they are able to prevent air that is being transferred to the downstream side from reversely passing over screw threads (36) from the downstream screw grooves (37) to the upstream side.
Air (high-density air), compressed by the turbo-molecular type pump air transfer portion (S2) disposed at the upstream side of the screw type air transfer portion (S1), flows into the upstream edge of the screw type transfer portion (S1), so that the screw type pump air transfer portion (S1) is able to perform air transfer under the same conditions as when it transfers air in low vacuum zones including atmospheric pressure zones (high air density zones). The screw type pump air transfer portion (S1) has the same air evacuation capacity in low vacuum zones including atmospheric pressure zones as ordinary screw type pumps, and is, thus, capable of exhausting the air (having an enhanced density) which has been drawn in from the turbo-molecular type air transfer portion (S2) in a compressed state, in a very efficient manner.
As described above, in the multiple-type pump invention (P), according to the present invention, the turbo-molecular type pump air transfer portion (S2) is disposed at the upstream side (air intake opening side) portion of the screw type pump air transfer portion (S1) formed on the outer circumferential surface of rotor (H), where the air intake and evacuation volumes can be estimated, based on turbo-molecular design theory.
It is, therefore, possible to increase air evacuation velocity by enlarging the square area of the opening at the air intake side to a great extent in the free molecule zone, without degrading the compression capacity. For this reason, a multiple-type pump can be realized in which a great air evacuation velocity can be attained at a wide range of pressure from low vacuum zones including atmospheric pressure zones to high vacuum zones.